Abstract

The following articles are being highlighted as part of Circulation's Topic Review series. This series will summarize the most important manuscripts, as selected by the editors, published in Circulation and the Circulation subspecialty journals. The studies included in this article represent the most read manuscripts published on the topic of cardiovascular genetics in 2009 and 2010.

Association of AHSG Gene Polymorphisms With Fetuin-A Plasma Levels and Cardiovascular Diseases in the EPIC-Potsdam Study

Summary

Findings from animal in vivo and human adipocyte in vitro studies suggest an effect of fetuin-A on the induction of subclinical inflammation and cytokine expression, thereby supporting the assumption that fetuin-A is directly involved in the pathogenesis of cardiovascular disease (CVD). In humans, elevated circulating levels of fetuin-A in blood are associated with incident myocardial infarction (MI) and ischemic stroke, independently of established risk factors for CVD. By using a Mendelian randomization approach, we investigated whether the observed association reflects a causal relationship or whether elevated circulating fetuin-A is merely a marker of CVD. We observed that the expected risk for MI associated with 1 standard deviation increase in circulating fetuin-A due to genetic variants in the fetuin-A gene (AHSG) was very similar to the observed association between fetuin-A plasma levels and MI risk. These data provide strong support for a functional link between elevated circulating fetuin-A and MI risk.

Conclusions

These data provide evidence for the causal nature of the recently reported association between fetuin-A plasma levels and MI risk, thereby suggesting an involvement of fetuin-A in the pathogenesis of cardiovascular disease.1

Summary

Currently, clopidogrel is the most widely used P2Y12 antagonist that, when used in combination with aspirin, significantly reduces the risk of recurrent atherothrombotic events in patients with acute coronary syndrome and those who undergo percutaneous coronary interventions. However, a wide interindividual variability in clopidogrel response has been reported, and patients with suboptimal platelet inhibition may be at higher risk of atherothrombotic events. Studies that tested the hypothesis that the P2RY12 gene variants are a determinant of the large between-subject variability in the efficacy of clopidogrel treatment have shown conflicting results. However, these studies were relatively small, and they focused on the 3′ part of the P2RY12 gene. Therefore, we studied comprehensively the relations of common variation in the P2RY12 gene and platelet reactivity on clopidogrel treatment in 1031 patients with coronary artery disease scheduled for elective percutaneous coronary interventions. We performed platelet function measurements by means of ADP-induced light-transmittance aggregometry and a point-of-care VerifyNow P2Y12 assay. The main finding of our study is that 2 common haplotypes (each >20% frequency) were associated with a 5% lower on-treatment aggregation per haplotype allele (ie, an improved clopidogrel response). This study may contribute to an improved identification of patients at increased risk of atherothrombotic events due to suboptimal clopidogrel-induced platelet inhibition.

Conclusions

Common variation in the P2RY12 gene is a significant determinant of the interindividual variability in residual on-clopidogrel platelet reactivity in patients with coronary artery disease.2

Summary

Behavioral patterns may be indirect markers of harmful exposures, which could modify the effects of genes. In this study, we identified important genetic interactions of education and behavioral factors on blood pressure. In particular, we found evidence for distinct genetic effects on diastolic and systolic blood pressures among American Indians with different levels of smoking and alcohol intake, physical activity, and education. These interactions were identified for the combined effects of multiple genes (polygenic effect) affecting blood pressure. Because some of these behaviors are modifiable, their interaction with genetic susceptibility to hypertension is of substantial public health importance.

Conclusions

Our findings suggest that behavioral and socioeconomic factors can modify the genetic effects on blood pressure phenotypes. Accounting for context dependent factors may help us to better understand the complexities of the gene effects on blood pressure and other complex phenotypes with high levels of genetic heterogeneity.3

Association of Blood Lipids With Common DNA Sequence Variants at 19 Genetic Loci in the Multiethnic United States National Health and Nutrition Examination Survey III

Summary

A principal goal of genetic association studies has been to augment current disease prediction algorithms by identifying genetic variants associated with common diseases. Genome-wide association studies along with candidate gene studies have identified many variants associated with plasma lipid traits. However, most genome-wide association studies published to date and most candidate gene studies have been conducted exclusively in samples of European ancestry. Therefore, it is unclear whether these variants are relevant in a broader range of ethnic groups such as blacks and Hispanic Americans. In the current study, we tested polymorphisms from candidate gene loci and loci identified through genome-wide association in the Third United States National Health and Nutritional Examination Survey, a population-based probability sample consisting of non-Hispanic black, Mexican American, and non-Hispanic white participants. Our study takes the first step toward addressing whether the same genetic variants identified in populations of European ancestry will be associated with blood lipids and, therefore, possibly predictive in other ethnic groups. Although further work is needed, our findings suggest that for many loci, the same variant identified in whites will also be relevant in other ethnic groups.

Conclusions

At 5 loci including the recently discovered region on 1p13 near CELSR2/PSRC1/SORT1, the same SNP discovered in whites associates with blood lipids in non-Hispanic blacks and Mexican Americans. For the remaining loci, fine mapping and resequencing will be required to definitively evaluate the relevance of each locus in individuals of African and Hispanic ancestries.4

Summary

Congestive heart failure is a leading cause of morbidity and mortality worldwide. Over the past decade, one of the most significant therapeutic advances in heart failure treatment has been biventricular pacing (cardiac resynchronization therapy [CRT]). CRT can both acutely and chronically increase systolic function, improve the efficiency of contraction, and prolong survival in patients with left-sided intraventricular conduction delay. However, the mechanisms underlying the benefit of CRT remain elusive. By using microarray-based studies of gene expression, we provide for the first time detailed and comprehensive insights into the transcriptional processes associated with dyssynchronous electromechanical activation. These experiments were conducted in a well-controlled large animal model, enabling tissue sampling from early-activated anterior and late-activated lateral left ventricular regions in dyssynchronous heart failure. As a result, we report a profound effect of electromechanical dyssynchrony on the regional cardiac transcriptome. Moreover, we show that, by recoordinating contraction, the heterogeneity of gene expression can be greatly reduced, even in a failing heart, on a genome-wide level. This may point to a more biological method to assess the impact of CRT. A better understanding of the molecular processes associated with the reverse remodeling in CRT will help to optimize and refine patient selection, device settings, and outcome assessment.

Conclusions

Our results demonstrate a profound effect of electromechanical dyssynchrony on the regional cardiac transcriptome, causing gene expression changes primarily in the anterior LV wall. CRT corrected the alterations in gene expression in the anterior wall, supporting a global effect of biventricular pacing on the ventricular transcriptome that extends beyond the pacing site in the lateral wall.5

Genetic Ancestry Is Associated With Subclinical Cardiovascular Disease in African-Americans and Hispanics From the Multi-Ethnic Study of Atherosclerosis

Summary

The burden of cardiovascular disease (CVD) disproportionately affects certain racial/ethnic groups. Many previous studies have shown that subclinical CVD measures such as coronary artery calcium (CAC) and carotid intima media thickness (cIMT) are associated with clinical CVD events. The presence and amount of subclinical cardiovascular disease (as measured by indicators such as CAC and cIMT) differ by race or ethnicity; white persons have higher CAC prevalence, and African-Americans have greater common cIMT, whereas Hispanic persons tend to have less CAC than white but greater cIMT than African-Americans. Our findings show that among African-Americans, the greater the amount of European ancestry, the higher the prevalence of CAC. The higher levels of European ancestry were also associated with lower common cIMT. Among Hispanics, higher amounts of European (and possibly Native American) ancestry corresponded to greater CAC prevalence. Furthermore, among African-Americans, the findings suggest that this relationship (between genetic ancestry and CAC prevalence) is a graded and linear one, whereas among Hispanics, a certain threshold or level of a particular ancestral background may be more relevant. These findings may be clinically relevant because they demonstrate that subclinical CVD can vary across the spectrum of a particular ancestral background, even after statistical adjustment for traditional CVD risk factors (such as age, sex, lipid levels, smoking, body mass index, diabetes, hypertension, kidney disease, as well as other important socioeconomic differences). Thus, even within a self-reported race group, patients can and likely will have wide variability in the prevalence of different subclinical CVD measures, which is at least partially dependent on ancestral background.

Conclusions

The linear association of ancestry and subclinical CVD suggests that genetic effects may be important in determining CAC and carotid intima media thickness among African-Americans. Our results also suggest that CAC and common carotid intima media thickness may be important phenotypes for further study with admixture mapping.6

Echocardiographic Strain Imaging to Assess Early and Late Consequences of Sarcomere Mutations in Hypertrophic Cardiomyopathy

Summary

Hypertrophic cardiomyopathy (HCM) provides a paradigm for using genetic discoveries to better predict and prevent disease. HCM is caused by mutations in sarcomere genes, resulting in left ventricular hypertrophy (LVH) and an increased risk of heart failure and arrhythmias. Genetic testing allows identification of a unique cohort of sarcomere mutation carriers (G+) who have not yet developed traditional phenotypic manifestations of disease (LVH- denoted preclinical HCM). By studying preclinical HCM, early manifestations of sarcomere mutations can be characterized, before pathological cardiac remodeling. To investigate the early and late consequences of sarcomere mutations on cardiac function, echocardiographic strain in preclinical HCM was compared with overt HCM and normal controls. The authors report different patterns of LV contractile abnormalities in early versus late disease. Preclinical HCM is characterized by LV diastolic dysfunction with preserved systolic strain. In contrast, both diastolic and longitudinal LV systolic function is significantly reduced in overt HCM despite normal LV ejection fraction. They propose that although LV diastolic dysfunction occurs as an early consequence of the underlying sarcomere mutation, systolic dysfunction results from the mutation in combination with the distinctive changes in myocardial architecture that accompany clinical disease. These results have potentially important clinical implications because they raise the possibility that future treatment to diminish the development of myocyte disarray, fibrosis, and hypertrophy, starting in the preclinical stage, may attenuate loss of LV systolic function and retard progression to symptomatic heart failure in HCM, a premise that warrants further study. Identifying mechanistic pathways triggered by sarcomere mutations may begin to reshape paradigms for clinical treatment of HCM, including strategies for early diagnosis and disease prevention.

Conclusions

Sarcomere mutations have disparate initial effects on diastolic and systolic functions. Preclinical HCM is characterized by impaired relaxation but preserved systolic strain. In contrast, both diastolic and longitudinal systolic abnormalities are present in overt disease despite normal ejection fraction. We propose that diastolic dysfunction is an early consequence of sarcomere mutations, whereas systolic dysfunction results from mutations combined with subsequent pathological remodeling. Identifying mechanistic pathways triggered by these mutations may begin to reshape the clinical paradigm for treatment, based on early diagnosis and disease prevention.7

Desmoglein-2 and Desmocollin-2 Mutations in Dutch Arrhythmogenic Right Ventricular Dysplasia/Cardiomypathy Patients: Results From a Multicenter Study

Summary

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is most often an autosomal dominantly inherited cardiomyopathy with primarily right ventricular involvement. Clinical presentation of ARVD/C could be highly variable but is characterized mainly by ventricular arrhythmias, syncope, and sudden cardiac death. The condition is uncommon (estimated prevalence ranging from 1 in 2000–1 in 5000 in the general population), and the diagnosis is based on criteria proposed by a task force (TFC). In this multicenter study from The Netherlands, the investigators systematically evaluated a large number of ARVD/C patients; they screened 116 patients (57 were TFC+) for mutations in 3 cardiac desmosomal genes (PKP2, DSG2, and DSC2). Mutations in PKP2 gene were most prevalent in TFC+ patients; nearly half (40%) of the TFC+ ARVD/C patients harbored a mutation in the PKP2 gene. The investigators found DSG2 and DSC2 mutations in ≈10% of TFC+ patients. Mutations in DSG2 and DSC2 also were observed in ≈10% of probable ARVD/C patients. Intriguingly, compound heterozygous mutations and mutations in both DSG2 and DSC2 genes were exclusively detected in TFC+ patients, suggesting a dose effect of mutations correlating with disease severity, although larger studies are needed to confirm this observation.

Conclusions

Mutations in DSG2 and DSC2 are together less prevalent (10%) than PKP2 mutations (40%) in Dutch TFC+ ARVD/C patients. Interestingly, biallelic or digenic DSC2 and/or DSG2 mutations are frequently identified in TFC+ ARVD/C patients, suggesting that a single mutation is less likely to cause a full-blown ARVD/C phenotype. Negative T waves on ECG were prevalent among mutation carriers (P<0.002).8

Summary

Calcific aortic stenosis (AS), the most frequent heart valve disorder, is a growing health problem with major societal and economic impacts. Previous attempts to slow the progression of AS by pharmacotherapy have failed, and aortic valve replacement remains the only efficient treatment for severe symptomatic patients. Elucidating the molecular mechanisms of calcific AS is crucial to develop efficient preventive or therapeutic strategies. Previous studies implicate active molecular and cellular processes in the pathogenesis of calcific AS. In this study, we expand this knowledge by using a genomic approach that tested the expression of most of the known genes simultaneously in aortic valves of patients with or without calcific AS. The data set that we generated constitutes the first large-scale quantitative measurements of gene expression in normal and stenotic human valves. By comparing the gene expression levels of the 2 groups, we identified genes that are perturbed in stenotic valves. These genes were overlaid on biological processes that are known to be involved in calcific AS to confirm, refine, and comprehensively complement our molecular understanding of this disease. This study also identified novel genes and pathways that are potentially implicated in calcific AS. In particular, this study demonstrates that MMP12 and CHI3L1 are upregulated in stenotic valves. These 2 genes had not been reported in previous investigations and constitute new targets to understand the pathogenesis of calcific AS.

Conclusions

This study reveals many unrecognized genes potentially implicated in the pathogenesis of AS. These new genes were overlaid on known pathological pathways leading to AS to refine our molecular understanding of this disease.9

Sarcomere Mutations in Cardiomyopathy With Left Ventricular Hypertrabeculation

Summary

Mutations in the gene encoding the sarcomere have been linked to hypertrophic and dilated cardiomyopathy. Recently, mutations in MYH7, ACTC, and TNNT2 have been reported in families and sporadic individuals with left ventricular noncompaction, a disorder where there is hypertrabeculation of the left ventricle and cardiomyopathy. Normally, during heart development, the left ventricle is transiently heavily trabeculated to allow for oxygenation before formation of the coronary arteries. Following vascular development, the inner layer of the left ventricle remodels into the mature compacted appearance. Persistence of deep trabeculae in a postnatal heart is variable, but in its severe form, left ventricular noncompaction can be associated with heart failure and thromboembolic events. We implemented clinically available genetic testing in 3 patients with left ventricular noncompaction cardiomyopathy. Two of these individuals were children and 1 was an adult with similarly afflicted family members. We found dominant mutations in MYH7 in 2 of the individuals, including the family with adult and pediatric affected members. In the third individual, we identified 2 different MYBPC3 mutations carried on different chromosomes, consistent with a complete absence of normal myosin-binding protein C. The myocardium from this individual had an absence of discernable M lines, now implicating cardiac myosin-binding protein C as a potential gene for left ventricular noncompaction. These findings suggest that individuals with hypertrabeculation and cardiomyopathy could be considered for screening for the presence of sarcomere mutations.

Conclusion

Genetic testing should be considered for cardiomyopathy with hypertrabeculation.10

General Cardiovascular Risk Profile Identifies Advanced Coronary Artery Calcium and Is Improved by Family History: The Multiethnic Study of Atherosclerosis

Summary

Coronary artery calcium (CAC) provides prognostic information regarding the risk of cardiovascular events. As a result, the presence of advanced CAC has been proposed as a rationale for aggressive risk factor modification. Using the data from the Multiethnic Study of Atherosclerosis, we assessed the ability of the General Cardiovascular Risk Profile (GCRP) to identify individuals with advanced CAC and determined whether identification of advanced CAC is improved by adding 2 different definitions of a positive family history of coronary heart disease. We defined family history as a dichotomous variable (ie, having at least 1 first-degree relative with premature coronary heart disease) or by familial risk stratification (ie, as a weak, moderate, or strong family history based on number of relatives with coronary heart disease, age at onset, and the presence of stroke or diabetes in the family). We observed that the GCRP worked well to identify individuals with positive CAC scores, and the addition of family history using either definition improved the discriminatory ability of this model. However, correct reclassification of individuals into lower or higher risk categories for a CAC score >300 was only improved with the addition of familial risk stratification to the GCRP variables. Our findings are consistent with the notion that the GCRP is a general model for assessing global cardiovascular disease risk, and we demonstrate that addition of family history to the GCRP (especially comprehensive familial risk assessment based on the number of relatives with coronary heart disease, age at onset, and the presence of stroke or diabetes in the family) further enhances the prediction of the presence of advanced CAC.

Heterogeneity of Genetic Modifiers Ensures Normal Cardiac Development

Summary

Individuals who share the same underlying basis for congenital heart disease can have presentations ranging from normal to life-threatening. Understanding the basis of such wide variability could suggest prognostic and therapeutic strategies focused not on the causes but on the modifiers of disease. We thus characterized the effect of genetic modifiers on the incidence of heart defects associated with mutation of the cardiac transcription factor Nkx2–5. Quantitative analyses of multiple inbred mouse strain crosses reveal the profound effect of polymorphic genetic modifiers. Protective and susceptibility alleles of modifier loci direct the manifestation of 1 or more types of heart defects, suggesting that they affect the sensitivity of specific cardiac developmental pathways to a perturbation. The modifiers alter the risk of a particular phenotype either independently or via epistatic interactions with other loci. The results intertwine the genetic basis of health and congenital heart disease, providing a conceptual framework to understand common clinical observations related to incomplete penetrance and pleiotropy. We propose that stabilizing selection generated a diverse set of polymorphisms so that in a genetically heterogeneous population the predominant effect of modifier genes is to ensure the robustness of cardiac development.

Conclusions

Alleles of modifier genes can either buffer perturbations on cardiac development or direct the manifestation of a defect. In a genetically heterogeneous population, the predominant effect of modifier genes is health.12

A Common Copy Number Variation on Chromosome 6 Association With the Gene Expression Level of Endothelin 1 in Transformed B Lymphocytes From Three Racial Groups

Summary

Copy number variation (CNV) may influence cardiovascular disease risk through potential biological effects on various cardiovascular disease candidate genes. One plausible mechanism is an effect of CNV on gene expression levels of candidate genes. We studied the association between 1529 CNV regions on 22 autosomes and gene expression levels of 7 genes in the endothelin system. The endothelin system is implicated in hypertension, heart failure, atherosclerosis, chronic kidney disease, and diabetes. Two hundred seventy subjects from 3 racial groups in the HapMap project had mRNA gene expression data for endothelin-1, endothelin-2, endothelin-3, endothelin converting enzyme 1, endothelin converting enzyme 2, endothelin receptor type A, and endothelin receptor type B and genotype data from the Affymetric 6.0 chip. Gene expression was measured in transformed B lymphocytes. The strongest association was between a 66 kbp CNV region on chromosome 6 and endothelin-1 expression. This CNV explained between 7% and 14% of the variation in endothelin-1 expression in the 3 racial groups. Because CNVs have large base-pair coverage in the human genome, their functional roles in development of human disease are substantial. Importantly, ongoing genome wide association studies provide the opportunity to study genome wide CNV association with candidate genes to help expand our understanding of the genetic architecture of cardiovascular disease and identify high-risk individuals as well as targets for prevention and therapeutic interventions.

Conclusions

Although the biological function of the chromosome 6 CNV is unclear, the significant and consistent association found in 3 racial groups suggests that CNVs may contribute to variation in underlying risks of common disease through their effects on key molecular signaling pathways.13

Growth-Differentiation Factor-15 for Risk Stratification in Patients With Stable and Unstable Coronary Heart Disease: Results From the AtheroGene Study

Summary

The clinical presentation of patients with coronary heart disease (CHD) ranges from chronic stable angina to acute coronary syndrome (ACS). Within these broad patient categories, the future risk of adverse coronary events may vary considerably in individual patients. Growth-differentiation factor-15 (GDF-15) is a stress-responsive cytokine that is produced in the heart and in extracardiac tissues. Previous studies in highly selected ACS trial populations have documented a close association between the circulating levels of GDF-15 and mortality risk. We measured the circulating levels of GDF-15 in 2229 unselected, real-life CHD patients undergoing coronary angiography in 2 hospitals in Germany. Patients were followed for a median of 3.6 years. GDF-15 levels within the normal range (<1200 ng/L) were associated with a very low risk of CHD mortality at 3.6 years (1.4% in stable angina patients; 1.7% in ACS). Conversely, GDF-15 levels >1800 ng/L identified a patient subgroup at high risk of CHD mortality (15.0% in stable angina; 14.6% in ACS). After adjustment for age and gender, clinical variables, the number of diseased vessels, renal function, the levels of C-reactive protein, cardiac troponin I, and N-terminal pro-B-type natriuretic peptide, GDF-15 levels >1800 ng/L remained associated with 6.3- and 4.9-fold increases in the risk of CHD mortality in stable angina and ACS, respectively. Our study identifies GDF-15 as a promising new biomarker for risk stratification across a broad spectrum of patients with stable and unstable coronary heart disease.

Conclusion

This study identifies GDF-15 as a strong and independent predictor of CHD mortality across the broad spectrum of patients with stable and unstable CHD.14

Summary

Exon deletions of the dystrophin gene lead to Becker muscular dystrophy and X-linked dilated cardiomyopathy. Both conditions are associated with cardiomyopathy with variable onset between the second and sixth decade of life. Better understanding of the predictive pathogenic factors influencing time of onset and severity of cardiac involvement would enable clinicians to begin early intervention, and potentially prevent premature death. In this study, insight into the evolution of cardiomyopathy was gained from analyzing a large patient population with the most prevalent exon deletions affecting discrete dystrophin protein domains. Four patient groups emerged from our study. Their expected ages of cardiomyopathy onset seem to be associated with the location of the exon deletion mutation and the effects on dystrophin protein structure. The complexity of our findings illustrates that dystrophin exon deletions must be correlated with protein structural alterations to predict outcomes. Prospective testing of these relationships potentially will empower clinicians to use genotype information to intervene more effectively in the treatment of patients with Becker muscular dystrophy or X-linked dilated cardiomyopathy. In addition, the findings pave the way for improvements on current therapeutic approaches targeting the heart in dystrophinopathies and may be valuable for patient stratification in clinical trials.

Conclusions

We identified specific regions of the dystrophin gene that when mutated predispose Becker muscular dystrophy patients to early-onset dilated cardiomyopathy. In addition, we propose that some mutations lead to early-onset dilated cardiomyopathy by specific alterations in protein folding. These findings have potential implications for early intervention in the cardiac care of Becker muscular dystrophy patients and for therapeutic approaches that target the heart in dystrophinopathies.15

Heart Failure–Associated Changes in RNA Splicing of Sarcomere Genes

Summary

Changes in gene expression accompany and contribute to heart failure. These gene expression changes have been documented at the whole-gene level using microarray-based, genome-wide expression profiling approaches. However, global changes in mRNA splicing in heart failure have not been previously studied. Here, we use a microarray that individually measures expression of each known or putative exon and reverse transcription polymerase chain reaction assays to examine splicing changes that accompany heart failure. We found that broad changes in mRNA splicing occur in the failing heart. Many of these changes were indicative of decreased efficiency of mRNA splicing, and among the affected genes, there were several sarcomere genes. These splicing changes also were observed in hypertrophied myocardium with preserved systolic function, suggesting that the splicing changes may occur before the onset of overt heart failure. The splicing changes were characteristic of diseased myocardium. A prediction model using the splicing of 3 sarcomere genes discriminated failing from nonfailing hearts with 98% accuracy, providing proof of principle that splicing-based biomarkers may provide diagnostic and prognostic information on patients with heart disease. Future studies will be needed to prospectively evaluate the value of splicing-based myocardial biomarkers in individualizing therapy in heart failure. Future work also will be needed to determine whether changes in RNA splicing are functionally important in the pathogenesis of heart disease and whether targeted modulation of splicing is a useful therapeutic strategy for heart failure.

Conclusions

Our data indicate that mRNA splicing is broadly altered in human heart disease and that patterns of aberrant RNA splicing accurately assign samples to control or disease classes.16

The FTO Gene Is Associated With an Atherogenic Lipid Profile and Myocardial Infarction in Patients With Type 2 Diabetes: A Genetics of Diabetes Audit and Research Study in Tayside Scotland (Go-DARTS) Study

Summary

Common variation in the FTO gene has recently emerged as a major determinant of human obesity. Obesity is, in turn, associated with an increased risk of developing type 2 diabetes with all its associated detriments to health. Recent evidence indicates that the FTO gene regulates obesity by modulating food preference, with a recent study showing that children aged 7 to 9 eat 100 extra calories at a single meal when they carry a particular FTO gene variant. These extra calories come from preferentially eating more energy-dense foods and may be mediated by differential regulation of hypothalamic gene expression by the protein encoded by FTO. In the current report, a group of patients being managed for type 2 diabetes who have inherited this same variant of the FTO gene that is associated with overeating are on average even more obese and have an unhealthier metabolic phenotype compared with patients not having this variant. This, in turn, leads to a greater risk of myocardial infarction and death. Therefore, this gene has an impact on individuals from early childhood through old age predisposing them to a greater risk of ill health probably largely through the eating habits it engenders. Interestingly, we find that in patients who have been prescribed lipid-lowering therapy in the form of statins this association is not evident. This suggests that variation in the FTO gene may contribute in the future to targeting specific therapies and interventions to those individuals at greatest risk.

Conclusion

The increased fat mass in carriers of the A allele of rs9939609 of FTO is associated not only with increased risk of type 2 diabetes, but also with an increase in atherogenic lipid profile and myocardial infarction in these patients. This variant may, therefore, in the future contribute to more effective targeting of specific preventative therapy.17

9p21 is a Shared Susceptibility Locus Strongly for Coronary Artery Disease and Weakly for Ischemic Stroke in Chinese Han Population

Summary

The results of this study extend the findings from recent genome-wide association studies that common genetic variants on chromosome 9p21 were strongly associated with increased susceptibility to coronary artery disease. Our data suggest that this locus is also associated with the risk of ischemic stroke in the Chinese Han population. Genetic variants may contribute to the estimation of the absolute risk of developing cardiovascular disease events when combined with traditional cardiovascular risk factors. However, it remains to be determined whether genetic variants on chromosome 9p21 would improve discrimination or classification of cardiovascular risk when combined with traditional risk factors in different populations. Therefore, the practical utility of our data needs further investigation.

Conclusions

Our results suggest for the first time that 9p21 is a shared susceptibility locus, strongly for CAD and weakly for ischemic stroke, in a Chinese Han population.18

Clinical and Functional Characterization of TNNT2 Mutations Identified in Patients With Dilated Cardiomyopathy

Summary

Rapid recent progress has been made to discover the genetic causes of dilated cardiomyopathy (DCM), and this new knowledge is now contributing to clinical practice. Because DCM usually presents with advanced, life-threatening disease, knowledge of a DCM-causing mutation in a family member of a patient diagnosed with DCM enables heightened clinical surveillance, and with evidence of early disease, medical and antiarrhythmic device therapy may prevent disease progression or life-threatening complications. One emerging issue in the molecular genetic diagnosis of DCM is ensuring that the sequence variation (commonly called a “mutation”) indeed is disease causing. This is particularly relevant for genetic DCM, as >30 genes have been implicated, and most mutations are unique to each patient and their family (“private” mutations). For DCM, these mutations can occur in many different coding locations of each gene, rendering the diagnosis challenging. This finding, termed locus heterogeneity, means that the entire coding sequence of each gene must be examined. With more sequence data available, there is greater likelihood of finding variations that may be difficult to determine whether they are actually relevant or causal for disease. This study examined mutations in the cardiac troponin T gene (TNNT2) with the mutant troponin T proteins reconstituted in an elegant system designed to detect contractile defects. The investigation illustrates the potential of functional studies to substantiate the evidence that putative disease-causing DCM mutations indeed are relevant for those family members in whom they may be detected.

Conclusions

We conclude that the combination of clinical, pedigree, molecular genetic, and functional data strengthen the interpretation of TNNT2 mutations in DCM.19

Clinical and Functional Characterization of TNNT2 Mutations Identified in Patients With Dilated Cardiomyopathy

Summary

Rapid recent progress has been made to discover the genetic causes of dilated cardiomyopathy (DCM), and this new knowledge is now contributing to clinical practice. Because DCM usually presents with advanced, life-threatening disease, knowledge of a DCM-causing mutation in a family member of a patient diagnosed with DCM enables heightened clinical surveillance, and with evidence of early disease, medical and antiarrhythmic device therapy may prevent disease progression or life-threatening complications. One emerging issue in the molecular genetic diagnosis of DCM is ensuring that the sequence variation (commonly called a “mutation”) indeed is disease causing. This is particularly relevant for genetic DCM, as >30 genes have been implicated, and most mutations are unique to each patient and their family (“private” mutations). For DCM, these mutations can occur in many different coding locations of each gene, rendering the diagnosis challenging. This finding, termed locus heterogeneity, means that the entire coding sequence of each gene must be examined. With more sequence data available, there is greater likelihood of finding variations that may be difficult to determine whether they are actually relevant or causal for disease. This study examined mutations in the cardiac troponin T gene (TNNT2) with the mutant troponin T proteins reconstituted in an elegant system designed to detect contractile defects. The investigation illustrates the potential of functional studies to substantiate the evidence that putative disease-causing DCM mutations indeed are relevant for those family members in whom they may be detected.

Conclusions

We conclude that the combination of clinical, pedigree, molecular genetic, and functional data strengthen the interpretation of TNNT2 mutations in DCM.19

Summary

The genes identified in this study as having similar expression profiles between adaptive and maladaptive stimuli of cardiac hypertrophy, which may have been overseen without the time-warping alignment to the state of hypertrophy, may be generically involved in profound mechanisms for the development of hypertrophy. They offer a starting point for understanding the mechanisms of mechanically induced cardiac remodeling, which could in turn lead to the development of diagnostic and treatment strategies for preventing the progression from cardiac hypertrophy to heart failure. Peptides, such as cardiac troponin I, have long been used to evaluate patients for the diagnosis of myocardial infarction. However, these peptides are not released from cardiac myocytes until late in the disease process after cell destruction has occurred. Using gene microarray expression studies, we may be able to identify proteins that are secreted early in the pathological response to stress before cell death occurs; these proteins could serve as biomarkers for the onset of maladaptive remodeling. Additionally, understanding the mechanisms underlying myocardial remodeling could yield insight for the development of therapeutic strategies that take advantage of these common processes to normalize stress in the myocardium before pathological remodeling mechanisms, such as fibrosis, are initiated.

Conclusions

This finding lends support to the notion of a generalized cardiac growth mechanism that is activated in response to mechanical perturbation. The common and unique genetic signatures of adaptive and maladaptive hypertrophy may be useful in the diagnosis and treatment of pathological myocardial remodeling.20

An Evaluation of Candidate Genes of Inflammation and Thrombosis in Relation to the Risk of Venous Thromboembolism: The Women's Genome Health Study

Summary

Venous thromboembolism is a major public burden worldwide, with an annual incidence of 1 to 3 per 1000. In addition to conventional risk factors (including immobilization and cancer) and genetic variation in biological pathways associated with hemostasis and thrombosis, inflammatory processes related to innate immunity has been recently suggested to play a role. The present investigation, combining both an a priori selection of polymorphisms based on potential functionality and an a priori application of statistical approaches, has further implicated the importance of genetic variation within the inflammatory/immune cascade in the risk of incident idiopathic venous thromboembolism. Furthermore, it emphasizes the need of additional large-scale, prospective studies (including comprehensive genome-wide approach) to further elucidate the pathogenesis of incident venous thromboembolism. Although our present data have limited practical applicability, we believe they may point the way toward a future feasibility of creating comprehensive genetic risk factor panels and their application in clinical practice.

Conclusion

In addition to previously reported polymorphisms associated with hemostasis and thrombosis, these prospective cohort data suggest that genetic variation in IL-1 β and IL-10 genes may also influence the risk of idiopathic venous thromboembolism.21

High Incidence of the Cardiac Variant of Fabry Disease Revealed by Newborn Screening in the Taiwan Chinese Population

Summary

This study in the Taiwan Chinese population demonstrates the feasibility of a large-scale neonatal screening program for Fabry disease. The incidence of Fabry mutations among newborns was unexpectedly high (≈1 in 1400 male newborns), as was the prevalence of the cardiac variant mutation IVS4+919G→A. Awareness of this information may be important for physicians evaluating Chinese patients with hypertrophic cardiomyopathy because some patients could represent cardiac Fabry disease. The early identification of Fabry disease may allow timely therapeutic intervention with enzyme replacement therapy, possibly resulting in better clinical outcome.

Conclusion

We found an unexpected high prevalence of the cardiac variant Fabry mutation IVS4+919G→A among both newborns (≈1 in 1600 males) and patients with idiopathic hypertrophic cardiomyopathy in the Taiwan Chinese population. The early identification of undiagnosed patients allows timely therapeutic intervention providing a better clinical outcome.22

Summary

Vessel wall calcification and aneurysms often coexist. Our studies in mouse animal models now reveal that medial calcification and medial disruption share genetic determinants. Thus, in a genetic cross in mice, we mapped 3 loci that contributed to both traits and 2 additional loci specific for medial calcification. Using a systems genetics approach, we identified a number of candidate genes at these loci. One candidate, the ABCC6 transporter, was confirmed by transgenic complementation to contribute to medial aortic calcification. Understanding the molecular genetic factors contributing to arterial wall changes could potentially lead to novel diagnostic and therapeutic approaches.

Conclusions

Our data indicate that calcification, though possibly contributory, does not always lead to medial disruption and that in addition to aneurysm formation, medial disruption may be the precursor to calcification.23

HFE C282Y Homozygosity Is Associated With Lower Total and Low-Density Lipoprotein Cholesterol: The Hemochromatosis and Iron Overload Screening Study

Summary

Total cholesterol and LDL were found to be significantly lower in patients that were homozygous for the C282Y mutation of the hemochromatosis (HFE) gene in the Hemochromatosis and Iron Overload Screening (HEIRS) Study. The HEIRS study was a multi-ethnic North American study that screened 99, 711 participants for iron overload and HFE mutations. Mechanisms for this potential inverse association are unknown.

Conclusions

Total mean serum cholesterol and low-density lipoprotein levels were lower in C282Y homozygotes than in HFE wild-type participants. Further studies are required to determine whether this is related to iron overload, HFE alleles, or other factors on C282Y-positive chromosome 6p haplotypes.24

Serotonin Transporter Gene, Depressive Symptoms, and Interleukin-6

Summary

There is growing evidence that depression is associated with increased levels of inflammatory markers, but whether this link is casual remains speculative. We sought to determine whether a common genetic vulnerability may be an alternative explanation for the observed association between depression and inflammation. Consistent with this hypothesis, in a study of middle-age male twins, we found that the serotonin transporter gene (SLC6A4) is a common precursor of both depressive symptoms and circulating interleukin-6 levels. Approximately 10% of the correlation between these 2 phenotypes can be explained by the SLC6A4 genetic variants. Our results provide important insight into the role of serotonin in the pathophysiology of both depression and inflammation.

Conclusions

Genetic vulnerability involving the SLC6A4 gene is significantly associated with both increased depressive symptoms and elevated IL-6 plasma levels. Common pathophysiological processes may link depression and inflammation, and implicate the serotonin pathway in neural-immune interactions.25

Summary

One of the limitations of cardiac resynchronization therapy is that 20% to 30% of the patients demonstrate little clinical benefit, if any at all. We believe that insight regarding the molecular mechanisms that are activated by cardiac resynchronization therapy may provide candidate targets that identify responders to this therapy and that proteomics could help in pinpointing the key proteins in this process and could narrow down the search for pathways that are dysregulated in nonresponders. Additionally, the study explores what the beneficial pathways activated by cardiac resynchronization therapy are in a well-established in vivo model.

Conclusions

Recurrence of Discordant Congenital Heart Defects in Families

Summary

Select congenital heart defects (CHD) could be similar in etiology and therefore might aggregate in families. In contrast to previous studies of familial aggregation of CHD, the present nationwide study evaluated familial aggregation for all pairwise combinations of discordant CHD phenotypes (heterotaxia, conotruncal defects, atrioventricular septal defects, anomalous pulmonary venous return, left- and right-ventricular outflow tract obstruction, isolated atrial septal defect, isolated ventricular septal defect, complex defects, associations, persistent ductus arteriosus, other specified CHD, and unspecified CHD) by investigating an individual's risk of being born with a CHD given one or more different CHD in first-degree relatives. For many combinations, the relative risk—here a measure of familial aggregation of discordant CHD within families—suggested that individuals with a family history of CHD in first-degree relatives had a 2- to 4-fold increased risk of CHD compared with individuals without a family history of CHD. Interestingly, we found no evidence that specific combination of the 14 CHD phenotypes aggregated in families. Furthermore, minor CHD among first-degree family members did not insulate against severe defects in subsequent relatives. Overall, the familial aggregation of discordant CHD is unlikely to be exclusively environmental in origin but probably has genetic origins as well.

Conclusion

We documented strong familial aggregation of discordant CHD phenotypes. However, we observed no excess clustering of specific CHD phenotypes among the first-degree relatives.27

A Genome-Wide Association Scan of RR and QT Interval Duration in 3 European Genetically Isolated Populations: The EUROSPAN Project

Summary

Higher heart rate at rest (which is equivalent to a shorter RR interval) has been associated with an increased risk of cardiovascular disease and with an increased mortality from cardiovascular disease. Given the importance of heart rate as an independent predictor of cardiovascular disease and death, it is important to identify genetic variants that influence resting heart rate. Such knowledge may provide new insights into physiological pathways involved in control of sinus rhythm and the etiology of heart disease itself, which could promote the development of appropriate prevention strategies and identification of targets suitable for drug development. Our findings suggest that GPR133, a member of the G-protein–coupled receptor family, plays a role in determining the heart rate. Because β-adrenergic receptors are members of this G-protein–coupled receptor family and are targeted by β-blocker drugs in the management of cardiac arrhythmias, GPR133 could represent a promising candidate for testing in future pharmacological approaches.

Conclusion

Our results suggested an association between the RR interval and GPR133 and confirmed an association between the QT interval and NOS1AP.28

Summary

Plasma levels of homocysteine are modulated by nutritional (including deficiency of vitamin B12 and folate) and genetic factors. Nutritional supplementation, frequent in the developed world, may mask genetic effects in such populations. Because the strict vegetarian diet of most Indians predisposes them to vitamin B12 deficiency, single-nucleotide polymorphisms in genes involved in homocysteine metabolism may have a greater effect on plasma homocysteine levels. In this study, we genotyped 44 nonsynonymous single nucleotide polymorphisms present in 11 genes involved in homocysteine metabolism and related them to plasma homocysteine levels. We found that polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) and choline dehydrogenase (CHDH) genes were associated with plasma homocysteine levels. Although several studies have shown that individuals with 677TT variant in the MTHFR gene have higher homocysteine levels, particularly in the setting of a low folate status, the association of 119CC variant in CHDH gene with plasma homocysteine levels has not been previously reported. In this study, we also determined the frequency of various nonsynonymous single nucleotide polymorphisms in genes involved in homocysteine metabolism. We studied at least 24 different subpopulations spread across the India based on their linguistic lineages and ethnic background.

Conclusion

Vegetarian diet along with CHDH A119C and MTHFR C677T play an important role in modulating the homocysteine levels in Indian population.29

In Vivo Genetic Evidence for Suppressing Vascular and Soft-Tissue Calcification Through the Reduction of Serum Phosphate Levels, Even in the Presence of High Serum Calcium and 1,25-Dihydroxyvitamin D Levels

Summary

In this study, we have shown that serum phosphate levels are an important in vivo determinant of vascular calcification and that lowering serum phosphate levels can reduce or eliminate soft-tissue and vascular calcification, even in the presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. Hyperphosphatemia and reduced serum levels of 1,25-dihydroxyvitamin D are the major biochemical changes detected in patients with chronic kidney disease. The current treatment approach of reducing serum phosphate levels and providing vitamin D analogs in patients with chronic kidney disease often poses a dilemma because vitamin D treatment is often linked to subsequent vascular calcification. Of relevance, ≈50% of mortality in patients with chronic kidney disease undergoing dialysis treatment is due to cardiac complications, including coronary calcification. Our current study provides evidence for the in vivo beneficial effects of reducing serum phosphate levels that prevented or reduced vascular calcification, even in the presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. These results provide compelling genetic evidence that suggests that reducing “phosphate toxicity” should be a critical therapeutic priority for minimizing the risk of vascular calcification and disease progression.

Conclusion

Our in vivo genetic manipulation studies have provided compelling evidence for a pathological role of increased NaPi2a activities in regulating abnormal mineral ion metabolism and soft-tissue anomalies in klotho-/- mice. Notably, our results suggest that serum phosphate levels are the important in vivo determinant of calcification and that lowering serum phosphate levels can reduce or eliminate soft-tissue and vascular calcification, even in presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. These in vivo observations have significant clinical importance and therapeutic implications for patients with chronic kidney disease with cardiovascular calcification.30

A Common Variant of the FTO Gene Is Associated With Not Only Increased Adiposity but Also Elevated Blood Pressure in French Canadians

Summary

FTO is one of several genes associated with common forms of obesity. The gene is highly expressed in the hypothalamus, where it is thought to mediate this effect through its influence on appetite-regulating regions. The hypothalamus, however, is also a powerful regulator of sympathetic outflow to the circulatory system and maintenance of blood pressure (BP). Consistent with possible influence of FTO on both adiposity and BP, the results of this study carried out in a French Canadian founder population suggest that FTO may increase not only likelihood of developing obesity, as demonstrated previously in other populations, but also hypertension. The results also suggest that FTO may influence BP and adiposity independently and that the FTO influence on BP may be mediated, at least in part, by its association with sympathetic modulation of vasomotor tone. The FTO association with BP was identified in adolescents and confirmed in an independent sample of adults, with adjusted BP differences between risk and nonrisk genotypes being >4 mm Hg in adolescents and >7 mm Hg in adults. These results raise the possibility that that individuals with an FTO variant that is associated with increased risk of hypertension may be recognized early before the onset of elevated BP and targeted with preventive measures.

Conclusions

These results suggest that, in a French Canadian founder population, FTO may increase not only risk for obesity, as demonstrated in other populations, but also for hypertension. The latter may be related, at least in part, to the regulation of sympathetic vasomotor tone.31

Summary

Several studies have focused on discovering the genetic causes of dilated cardiomyopathy (DCM) that occurs in families (familial DCM). Mutations in >30 genes have now been shown to be associated with DCM. To extend our understanding of DCM genetics, we conducted resequencing studies (where the DNA samples from patients with DCM were sequenced for nucleotide variation in selected genes) in a large cohort of patients with familial DCM and in patients with apparently nonfamilial DCM of unknown cause (idiopathic DCM). In this study, 5 sarcomeric genes were resequenced in 312 DCM probands, 181 with familial DCM, and 131 with idiopathic DCM. Variants that were considered rare (ie, not present in 492 chromosomes from control subjects) and that changed highly conserved amino acids or affected intron/exon splicing were identified in 34 probands (10.9% overall). These variants were classified as likely disease causing in 13 or possibly disease causing in 20 probands and included 12 MYBPC3(myosin-binding protein C) in 13 (4.2%) probands, 8 MYH6 (α-myosin heavy chain) in 10 (3.2%), 6 TPM1 (tropomyosin) in 6 (1.9%), 4 TNNC1 (cardiac troponin C) in 4 (1.3%), and 1 TNNI3 (cardiac troponin I) in 2 (0.6%). A similar fraction of rare variants were identified in familial DCM and idiopathic DCM, suggesting that idiopathic DCM also may have a genetic basis. This investigation, when combined with previous resequencing studies of 9 genes, suggests that 27% of DCM probands have had a possibly or likely genetic cause identified.

Conclusion

Rare variants in these 5 genes likely or possibly caused 10.6% of DCM in this cohort. When combined with our prior resequencing reports, ≈27% of DCM probands had possible or likely disease-causing variants identified.32

Summary

Cardiovascular risk factors are highly common among the Mexican population. Although epidemiological studies have pointed out the increasing prevalence of several forms of dyslipidemias, this population has been underinvestigated in genetic studies and to date no genome-wide association studies for lipids have been performed in Mexicans. It is important to establish whether confirmed loci have a consistent effect across ethnic groups, especially if they are to be used in cardiovascular risk assessment. Furthermore, studies in diverse populations, such as Mexicans, could also assist in fine mapping the actual susceptibility variants. This study evaluated whether 15 single-nucleotide polymorphisms surpassing genome-wide significant threshold for either high-density lipoprotein cholesterol or triglycerides in Caucasian genome-wide association studies also confer risk in the Mexican population. Association at nominal level (P≤0.05) was observed for 10 of the loci, of which half were also significant after adjusting for multiple comparisons (2.20×10-3 to 2.6×10-11) in the APOA5, CETP, GCKR, and GALNT2 gene regions. Our strongest signal was obtained for triglycerides with single-nucleotide polymorphism rs964184 (odds ratio, 1.74; P=2.6×10-11) in the APOA1/C3/A4/A5 gene cluster region that is significantly more prevalent in Mexicans (27%) than in whites (12%). Our data confirm that although variants may have effects across multiple ancestral groups, allele frequencies may have a major influence on the contribution of each locus to disease susceptibility and public health.

Conclusions

It is important to confirm whether known loci have a consistent effect across ethnic groups. We show replication of 5 Caucasian genome-wide association studies lipid associations in Mexicans. The remaining loci will require a comprehensive investigation to exclude or verify their significance in Mexicans. We also demonstrate that rs964184 has a large effect (odds ratio, 1.74) and is more frequent in the Mexican population, and thus it may contribute to the high predisposition to dyslipidemias in Mexicans.33

Novel Associations of CPS1, MUT, NOX4, and DPEP1 With Plasma Homocysteine in a Healthy Population: A Genome-Wide Evaluation of 13 974 Participants in the Women's Genome Health Study

Summary

Homocysteine is a sulfur amino acid whose plasma concentration has been associated positively with the risk of cardiovascular diseases, neural tube defects, and loss of cognitive function in epidemiological studies. Although genetic variants of 2 genes, MTHFR and CBS, are known to influence homocysteine concentration, other common genetic determinants of homocysteine remain largely unknown. In this report, we demonstrate that genetic variation at the CPS1, MUT, DPEP1, and NOX4 genes are also associated with plasma levels of homocysteine. These genetic associations provide novel insights into the biology of homocysteine. For instance, the CPS1 encodes a mitochondrial enzyme involved in the urea cycle Furthermore, the CPS1 genetic variant (rs7422339) associated with homocysteine in our study is also known from previous studies to be associated with nitric oxide metabolism, suggesting a possible link between homocysteine metabolism and endothelial function. DPEP1 and NOX4 are both expressed in kidneys and could potentially be involved in renal handling of homocysteine. The high levels of homocysteine observed in renal failure patients may imply a link between homocysteine and renal function. The novel associations observed in our investigation suggest this relationship may extend to healthy individuals as well.

Conclusions

These associations offer new insight into the biochemical pathways involved in homocysteine metabolism and provide opportunities to better delineate the role of homocysteine in health and disease.34

Common Coding Variants of the HNF1A Gene Are Associated With Multiple Cardiovascular Risk Phenotypes in Community-Based Samples of Younger and Older European-American Adults: The Coronary Artery Risk Development in Young Adults Study and The Cardiovascular Health Study

Summary

In several recent genome-wide analyses, common variants of the HNF-1α gene were associated with several circulating biomarkers related to cardiovascular risk, including C-reactive protein and γ-glutamyl transferase. Rare variants of HNF-1α previously have been shown to be associated with familial mature-onset diabetes of the young. Genetic coregulation by transcription factors such as HNF-1α might explain some of the correlation between atherosclerotic phenotypes, and variants of HNF-1α may contribute to the occurrence of more complex subclinical and clinical phenotypes, such as coronary atherosclerosis. Here, we confirm that common coding variants of HNF-1α are associated with multiple cardiovascular disease-related biomarkers and phenotypes including C-reactive protein, γ-glutamyl transferase, low-density lipoprotein cholesterol, fibrinogen, renal function, as well as risk of subclinical atherosclerosis and coronary disease in younger and older European-American adults, respectively. Identification of genetic markers that predict coronary disease may ultimately allow targeting of susceptible individuals for aggressive risk modification or drug therapy.

Conclusions

Common polymorphisms of HNF1A seem to influence multiple phenotypes related to cardiovascular risk in the general population of younger and older European-American adults.35

Evidence for Coregulation of Myocardial Gene Expression by MEF2 and NFAT in Human Heart Failure

Summary

Research in animals has shown that pathological stresses promote heart failure via activation of cardiac transcription factors. This process is complex, with each transcription factor responding to numerous stressors and each gene in turn coregulated by multiple transcription factors. Here, we used genomic approaches to explore whether this paradigm, identified in animal models, applies to human heart failure. Using gene-expression data from the failing human heart and data from publicly available sequence databases, we found that binding motifs for 5 “hypertrophic” transcription factors tended to cluster together in the promoters of cardiac genes. Furthermore, genes that contained binding motifs for both MEF2 and NFAT transcription factors showed a 3-fold increase in tendency toward altered expression in the failing heart. Thus, our study extends the paradigm of combinatorial regulation of gene expression to the failing human heart, and the specific transcription factor combinations and genes provide human targets for mechanistic study. More broadly, we demonstrate how integrating diverse sources of genomic data can yield novel insight into cardiovascular disorders.

Conclusions

These findings provide genomic evidence for coregulation of myocardial gene expression by MEF2 and NFAT in human heart failure. In doing so, they extend the paradigm of combinatorial regulation of gene expression to the human heart and identify new target genes for mechanistic study. More broadly, we demonstrate how integrating diverse sources of genomic data yields novel insight into human cardiovascular disorders.36

Summary

The Genetic Effects On STATins Study (GEOSTAT-1) highlights the variation in individual response to different statins. Patients with at least 1 variant copy of the genes that code for the liver enzyme CYP3A5 and/or the liver transporter breast cancer resistance protein (BCRP) were 2.3 times more likely to achieve the current LDL cholesterol target after myocardial infarction of 70 mg/dL, when prescribed rosuvastatin 10 mg compared with simvastatin 40 mg. This is consistent with recently published studies in which much higher rosuvastatin (and also atorvastatin) blood levels were observed in individuals with 1 or more variant copies of the breast cancer resistance protein gene variant. A potential clinical value of these findings might be the ability to use genetic information to optimize selection of statin subtype and dose to better avoid rare side effects that can occur with use of a higher statin dose. Such considerations would have particular relevance for the treatment of Asian patients, who are known to have a greater frequency of the breast cancer resistance protein gene variant and also higher blood concentrations after treatment with rosuvastatin. Awareness of a patient's genetic profile would also be expected to render safer and also more effective the use of rosuvastatin 20 mg in the clinical context of primary prevention of major cardiovascular events (as studied in the Justification for the Use of statins in Primary prevention Trial Evaluating Rosuvastatin [JUPITER] trial) and also the use of rosuvastatin 40 mg for reversal of coronary atheromatous plaque size (as demonstrated in the A STudy to Evaluate the effect of Rosuvastatin On Intravascular ultrasound-Derived coronary atheroma burden [ASTEROID] trial).

Conclusion

The LDL cholesterol target was achieved more frequently for the 1 in 3 patients with CYP3A5 and/or BCRP variant genotypes when prescribed rosuvastatin 10 mg, compared with simvastatin 40 mg.37

Genomic Variation Associated With Mortality Among Adults of European and African Ancestry With Heart Failure: The Cohorts for Heart and Aging Research in Genomic Epidemiology Consortium

Summary

This study investigated 2526 incident heart failure (HF) cases of European ancestry and 466 incident HF cases of African ancestry for an association between genome-wide variation and all-cause mortality. One variant in the CKLF-like MARVEL transmembrane domain containing 7 (CMTM7) genes was significantly associated with all-cause mortality in individuals of European ancestry with HF. CMTM7 is 1 of several chemokine-like factor genes clustered in the same region on chromosome 3p22. These results suggest that chemokines may play a role in survival of patients with HF. No genomic variation was significantly associated with mortality in individuals with HF of African ancestry. Future studies of this type may identify genes that lead to an improved understanding of HF pathophysiology and treatment of the disease. These findings warrant additional investigation, including replication, in other studies of HF.

Conclusions

This study identified a novel locus associated with all-cause mortality among individuals of European ancestry with HF. This finding warrants additional investigation, including replication, in other studies of HF.38

Association and Functional Analyses of MEF2A as a Susceptibility Gene for Premature Myocardial Infarction and Coronary Artery Disease

Summary

This investigation assessed the role of MEF2A gene in the pathogenesis of myocardial infarction (MI) and coronary artery disease (CAD). The involvement of this gene in the pathogenesis of CAD/MI has been long debated, but most reports have been genetic association studies. We conducted a functional analysis of previously known mutations in this gene that were reported to be associated with CAD/MI and also studied new genetic variants found in the gene in a large cohort of Italian patients with premature MI. Contrary to previously published work, our data do not support a causal role of MEF2A mutations in affecting the nuclear translocation or transactivation properties of mutant MEF2A proteins in a cellular model. Moreover, a microsatellite-based association analysis performed in the MI cohort and in a replication sample of Italian patients with CAD did not confirm an association of MEF2A with CAD/MI. Finally, the 21-bp in-frame deletion, originally associated with the CAD phenotype, was found in 5 cases and in 0 controls (MI cohort) and in 0 cases and 1 control (CAD cohort). These data, together with other recently published data, strongly argue against the hypothesis that genetic defects in MEF2A are directly involved in the pathogenesis of CAD/MI. Our results emphasize the importance of confirming “disease genes” for complex disorders both by replication of genetic associations and, whenever possible, by functional studies.

Conclusions

All together, our data do not support MEF2A as a susceptibility gene for coronary artery disease/MI in the Italian population.39

Comprehensive Analysis of Genomic Variation in the LPA Locus and Its Relationship to Plasma Lipoprotein(a) in South Asians, Chinese, and European Caucasians

Summary

Increased cardiovascular disease risk has been associated with plasma lipoprotein(a) [Lp(a)] levels, though somewhat inconsistently, limiting implementation in common clinical practice. Circulating concentrations of Lp(a) are largely under the control of genetic variation in the LPA gene due to the cumulative effects of multiple rare and common genetic variants. A common copy number variation in LPA, created by a variable number of exons coding for kringle IV type 2 domains, is known to affect Lp(a) concentration but, until recently, has not been measurable in cohorts with limited quantities of genomic DNA available. We demonstrate that a correlation exists between single-nucleotide polymorphisms in the LPA locus and kringle IV type 2 copy number and that both LPA single-nucleotide polymorphisms and kringle IV type 2 copy number contribute to Lp(a) concentration and, thus, should be measured in future studies of Lp(a). In agreement with previous work, the relationship between genomic variation in LPA and Lp(a) concentration appears to vary among ethnicities. Additional genetic variants that are too rare, have effects too small to be detected in the SHARE sample, or were not queried in this study, play a greater role in South Asians and Chinese. Further identification of rare and common variants is required in these and other ethnicities. Finally, our work shows that future Mendelian randomization studies investigating Lp(a) would benefit from including both LPA single-nucleotide polymorphisms and kringle IV type 2 copy number, as the extent of Lp(a) concentration explained is larger using both types of variation.

Conclusions

LPA SNPs are in linkage disequilibrium with KIV-2 copy number, but KIV-2 copy number explains an increment in plasma Lp(a) variation over SNPs alone. Thus, both SNPs and KIV-2 copy number should be included in future genetic epidemiology studies of Lp(a).40

Summary

Acute coronary syndrome (ACS) is accompanied by systemic changes in inflammation, coagulation, and metabolism, which may affect the outcome and prognosis of ACS. These systemic reactions are not explained by cardiac events alone. Several lines of evidence suggest that patients with fatty liver disease have a high risk of developing cardiovascular diseases, and it is possible to speculate that the liver is involved in a systemic reaction that modifies the pathogenesis of ACS. However, the relation between liver and myocardial ischemia in the acute ischemic phase has not been elucidated so far. In this investigation, we simultaneously analyzed the gene expression profiles of the liver and heart during acute myocardial ischemia in mice and observed the presence of humoral factors that intervened between the heart and liver. These humoral factors were released from the heart and influenced the liver to secrete important tissue remodeling factors. One of these humoral factors, osteopontin, a widely expressed glycoprotein, was increased in the ischemic heart and altered the gene expression of hepatocytes to produce important tissue remodeling factors (such as vascular endothelial growth factor-A). Our observations suggest that hepatic gene expression is potentially regulated by humoral factors of cardiac origin provoked by myocardial ischemia, and we provide direct evidence that the liver is involved in a systemic reaction that accompanies ACS. Our findings provide potential new insights into the pathophysiology of ACS.

Conclusions

Hepatic gene expression is potentially regulated by cardiac humoral factors under myocardial ischemia. These results provide new insights into the pathophysiology of acute coronary syndrome.41

Genetic Determinants of Major Blood Lipids in Pakistanis Compared With Europeans

Summary

Levels of the major blood lipids, LDL-C, HDL-C, and triglyceride are each strongly associated with the risk of coronary heart disease (CHD). Several genetic variants have been established in the regulation of lipid metabolism in people of European continental ancestry; however there are few data available on the genetic determinants of these lipid traits in South Asians a population with a high burden of cardiometabolic conditions. We investigated 45 000 variants across 2000 genes in 3200 Pakistanis, and 2450 Germans using the same gene array. A total of 41 variants at 14 loci, were found to be significantly associated with major lipid traits in Pakistanis, explaining 6.2%, 7.1%, and 0.9% of the variation in HDL-C, triglyceride, and LDL-C, respectively. The most significant lipid-related variants identified among Pakistanis corresponded to genes previously shown to be relevant to Europeans, such as CETP associated with HDL-C levels; APOA5/ZNF259 and GCKR with triglyceride levels; and CELSR2 variants with LDL-C levels. However, differing allelic frequencies and lipid effects for variants in APOA5 were observed in Pakistanis compared with Europeans. This study suggests that several lipid-related genetic variants are common to Pakistanis and Europeans, though they explain only a modest portion of population variation in lipid concentration. Allelic frequencies and the effect sizes of lipid-related variants can differ between Pakistanis and Europeans.

Conclusions

Several lipid-related genetic variants are common to Pakistanis and Europeans, though they explain only a modest proportion of population variation in lipid concentration. Allelic frequencies and effect sizes of lipid-related variants can differ between Pakistanis and Europeans.42

Identification of Genomic Predictors of Atrioventricular Conduction: Using Electronic Medical Records as a Tool for Genome Science

Summary

Three recent genome-wide association studies conducted in community populations have identified multiple loci contributing to variability in normal PR duration. This study sought to replicate these findings by performing a genome-wide association study in subjects identified in BioVU, the Vanderbilt DNA databank that accrues DNA from blood samples obtained during routine patient care and links these to a deidentified copy of the electronic medical record. Subjects were identified by combinations of natural language processing, laboratory queries, and billing code queries of medical record data. The genome-wide association study was conducted in 2334 European American patients with normal ECGs and no evidence of prior heart disease in the electronic medical record, and it confirmed a signal in a sodium channel gene, SCN10A, previously not implicated in cardiac pathophysiology as a modulator of PR interval in humans. This study is one of the first to validate use of an electronic medical records–derived cohort of genome-wide analysis, supporting their further use for genotype-phenotype analysis.

Conclusions

This genome-wide association study confirms a gene heretofore not implicated in cardiac pathophysiology as a modulator of PR interval in humans. This study is one of the first replication genome-wide association studies performed with the use of an electronic medical records–derived cohort, supporting their further use for genotype-phenotype analyses.43

. Association of blood lipids with common DNA sequence variants at 19 genetic loci in the multiethnic United States National Health and Nutrition Examination Survey III. Circ Cardiovasc Genet. 2009;2:238–243.

. A common copy number variation on chromosome 6 association with the gene expression level of endothelin 1 in transformed B lymphocytes from three racial groups. Circ Cardiovasc Genet. 2009;2:483–488.

. The FTO gene is associated with an atherogenic lipid profile and myocardial infarction in patients with type 2 diabetes: a Genetics of Diabetes Audit and Research Study in Tayside Scotland (Go-DARTS) study. Circ Cardiovasc Genet. 2009;2:255–259.

. In vivo genetic evidence for suppressing vascular and soft-tissue calcification through the reduction of serum phosphate levels, even in the presence of high serum calcium and 1,25-dihydroxyvitamin d levels. Circ Cardiovasc Genet. 2009;2:583–590.

. Common coding variants of the HNF1A gene are associated with multiple cardiovascular risk phenotypes in community-based samples of younger and older European-American adults: the Coronary Artery Risk Development in Young Adults Study and The Cardiovascular Health Study. Circ Cardiovasc Genet. 2009;2:244–254.

. Genomic variation associated with mortality among adults of European and African ancestry with heart failure: the cohorts for heart and aging research in genomic epidemiology consortium. Circ Cardiovasc Genet. 2010;3:248–255.

; SHARE Investigators.
Comprehensive analysis of genomic variation in the LPA locus and its relationship to plasma lipoprotein(a) in South Asians, Chinese, and European Caucasians. Circ Cardiovasc Genet. 2010;3:39–46.